ASCENDER

Ascender is a sub-orbital spaceplane from Bristol Spaceplanes carrying two crew and two passengers intended to provide proof-of-concept for the development of the Spacecab/Spacebus spaceplane, and is capable of reaching space (though not orbit). As well as being an entrant for the X-Prize, Ascender is intended to return commercial revenues through its passenger carrying capability.
SPACEBUS SPACECAB	Spacebus a design for a 2-stage passenger-carrying HTOL by the company Bristol Spaceplanes in Britain. The first stage uses jet engines for take-off, followed by rocket engines to climb to high altitude for separation, after which the upper stage uses rocket engines to reach orbit. This configuration has a number of advantages described at length in papers by David Ashford (including the recent "Space Tourism - How Soon Will it Happen?" and the 1990 book "Your Spaceflight Manual: How you could be a tourist in space within 20 years"). Using existing jet and rocket engines is very attractive in reducing initial development costs. And though new air-breathing rocket engines might be more efficient, they're not needed initially (the first stage just has to be a bit bigger and use a bit more fuel). And going high with the first stage makes separation easy as it's in thin air, so even hypersonic loads are small. Spacecab is a scaled-down version of Spacebus designed to carry 6 passengers. It's attractive as a first step to HTOL launch services since it uses only existing technology, and could start passenger operations much earlier than a vehicle requiring new engines to be developed.